It could be spit or miss, but researchers reported that TSP (thrombospondin), a natural sugar protein in human saliva, may block HIV from entering the body. "We began exploring why there is so little HIV in saliva," said Dr. Jeffrey Laurence of the Lab for AIDS Virus Research at New York Hospital. "This led to the discovery of TSP." What's up, doc? "In order for HIV to infect a cell in your body, it needs a door to get in -- and the major door is CD4. TSP blocks the ability of HIV to bind to that door by mounting a barrier."

The doc is developing a TSP-based cream or jelly to be inserted rectally or vaginally. TSP derivatives could potentially also be put in condoms, suppositories and mouthwashes. Laurence aims to test TSP on animals, but warned against hyping the power of saliva: "I don't want people to get the idea that you can spit on someone's rectum and prevent them from getting infected."